Today, with the advent of wireless technology, many aspects of everyday life can be controlled remotely. These include remote security systems, lighting systems, utility meter reading and many other applications.
Remote lighting systems have evolved and are able to not only remotely control turning on and off lighting, but also to control the intensity of the lighting.
FIG. 1A shows a conventional circuit used to control the brightness of a lighting system. A triac 10 is disposed in series between an AC power source 20 and the lighting 30. The gate of the triac 10 controls the passage of current between the AC power source 20 and the lighting 30. A positive or negative voltage (relative to the A1 terminal) applied to the gate triggers the triac 10 to conduct current between the A1 and A2 terminals. Once the triac begin conducting current, it will continue until the current between the A1 and A2 terminal drops below a certain threshold. Thus, once the gate voltage is applied, the triac 10 will conduct current until the next zero crossing, which is defined as the point at which the AC voltage crosses from positive to negative or negative to positive. Thus, by controlling the gate signal, the lighting system can be controlled. In its simplest form, the gate can be held at a low voltage to turn the lighting off, and held at a higher voltage to turn the lighting on.
FIG. 1B shows the gate voltage waveform that can be used to dim the lighting. In this example, the input to the A1 terminal (Vin) is a voltage in the form of a sine wave, as is typical of AC power sources. The A2 terminal is in electrical communication with the lighting 30. In this figure, the gate voltage is pulsed about 20% of a half-period after the zero crossing of the Vin input signal. At this point, current begins to flow through the triac 10, as shown in the Vout graph. Current continues to flow until the next zero crossing of the Vin signal. Thus, by varying the position of the gate pulse relative to the zero crossing, the amount of power delivered to the lighting 30 can be controlled.
While the above description utilizes a lighting system, it is noted that it is equally applicable to an AC power load that can accept a variable input, including electric motors.
While the circuit of FIG. 1A is power efficient and effective in controlling power delivered to a lighting system, it has some drawbacks. For example, variability in the assertion of the gate pulse relative to the Vm, can cause annoying flicker, which is perceivable to the human eyes. Therefore, an improved circuit for controlling the current supplied to a lighting system, or other electrical load, would be beneficial.